[gdal-dev] A strange thing with a png geospatial file and gdalwarp. Is it a bug?

[peifer]

aborruso wrote
> I have changed only the file format, and I obtain different results.
> 
> Is this normal?

It is "normal", because more than the format has been changed. Compare the
CRS definitions in png vs. tif and you'll find and additional extension
definition in the tif:

EXTENSION["PROJ4","+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0
+x_0=0.0 +y_0=0 +k=1.0 +units=m +nadgrids=@null +wktext  +no_defs"]

The above "auto-correction" includes the +nadgrids=@null parameter, which in
return avoids the "change of ellipsoid" step in the transformation.

Hermann



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